1. Field of the Invention
The invention relates to a polishing composition for chemical-mechanical polishing (CMP) of semiconductor substrates.
2. Description of Related Art
Chemical-mechanical polishing (CMP) refers to polishing of a semiconductor substrate to remove metal from an underlying dielectric layer of the semiconductor substrate, leaving the dielectric layer with a smooth, planar polished surface, and further leaving conducting circuit interconnects of metal that are imbedded in trenches in the dielectric layer below the smooth, planar polished surface.
A problem occurs when polishing to remove the metal from the underlying dielectric layer. The polishing operation tends to remove spots of metal, which exposes spots of underlying dielectric material. The polishing operation continues, and is known as overpolishing, to completely remove residual quantities of the metal from the underlying dielectric layer, which tends to remove some of the exposed dielectric layer from the semiconductor substrate, causing what is known as erosion. Such erosion of the dielectric layer adversely changes the critical dimensions along the trenches in the dielectric layer in which the circuit interconnects are imbedded. Erosion causes adverse changes to the critical dimensions and the electrical characteristics of the circuit interconnects.
Accordingly, a need exists for a polishing composition and a polishing method that minimizes removal of an underlying dielectric layer during a polishing operation that is performed to remove metal from the underlying dielectric layer.
U.S. 5,391,258 and 5,476,606 disclose a method for polishing a semiconductor substrate with a polishing pad and a polishing composition to remove metal from an underlying dielectric layer on the semiconductor substrate, and the polishing composition having a compound or compounds that suppress the removal rate of silica that comprises the underlying dielectric layer. The compound or compounds contain at least two acid groups of which the pKa of a first dissociable acid is not substantially larger than the pH of the polishing composition.